Leucine is a branched-chain essential amino acid. Its metabolism is linked to that of alanine and glucose. In pregnancy, the rate of gluconeogenesis is low, suggesting that muscle glycolysis should also be low, implying that glucose is spared for the fetus. The purpose of this protocol is to evaluate the question of where the mother gets her energy. Subject population consists of normal and diabetic pregnancies, and those complicated by intrauterine growth retardation.